New 1980 CB750F !!!

AdrianVall

Active Member
Hey all,

SUPER stoked here.. just came home with this gem. Found her about an hour from me. Seller wanted $1,500.. I got him down to $1,260 with a Clymers manual. I'm soooooooooo happy I found this. I've always wanted one of these. I haven't decided if I'm going to cafe it out or not, but I guess we shall see.

It needs a few things to get it going. I have to clean/rebuild the carbs. The front brake does not work.. needs a new master cylinder. Rear brake is sticking pretty bad.. gotta figure out what the deal is with that. Other then that, she runs! Idles fairly high and inconsistent, but it has a 4-1 Kerker exhaust and it sounds WICKED.

Anyway.. pics!

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Cheers,
Adrian
 
Thanks man! Appreciate those links. I'll have to check them out.

Does anyone know if the master cylinders from other CB750's fit the supersports? The F has dual front brakes, so I just want to make sure it'll fit.
 
Any MC with the same bore will work. It is usually stamped/cast on the underside of the MC body.

Nice stocker!


Keep an eye on the charging system, as they are known to not age well.


Enjoy!
 
Thanks for the help guys! Ordered me a new front brake cylinder and Carb rebuild kit with air cut off valves.. going to get them cleaned and rebuilt, and hopefully, I should have a good running bike! =)
 
tweeken is on here as well Adrian, he has build a bad ass couple of CB's, personally i would keep the seat cowl, but shave and reshape the seat, then recover it... that way you can still take your lady out riding... the passanger peg support mounts are huge and an eye sore, shoot those black so they blend in a bit more but shit that sucker is clean!!! as always man you need anything let me know!
 
JRK5892 said:
tweeken is on here as well Adrian, he has build a bad ass couple of CB's, personally i would keep the seat cowl, but shave and reshape the seat, then recover it... that way you can still take your lady out riding... the passanger peg support mounts are huge and an eye sore, shoot those black so they blend in a bit more but shit that sucker is clean!!! as always man you need anything let me know!

Yeah, I saw one of tweekens builds on here a while back. That thing was EPIC. What a great job he did. But yeah man, I'm definitely planning on keeping it a 2 up bike for the lady and I. I haven't decided if I'm going to keep the tail, or just take it all off and make a long straight, flat seat. I'm not sure where I'm going with it, but for now, I want to get it running nice so that I can get to riding again. I'm getting the itch REALLY bad.
 
i built a pretty bad ass brat seat for my goldwing build a while back pretty cheap and it looked great... you could do that as well

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Dude.. that goldwing was such a sick build.. did you ever sell it? Freakin' sweet man. But yeah, I've been playing with the idea of putting a brat style seat on. Not sure just yet. I just found a perfect condition, good running KZ 400 on craigslist that I may just pick up for my lady. That would be an awesome little scoot for her to learn to ride.
 
Well, need some help here..

Got the carbs rebuilt/cleaned, reinstalled, and now I'm leaking gas, from what looks like to be from one of the inside carbs. Only from that one carb. I tried tapping it thinking the float was stuck, but it didn't help. I turned the fuel valve off while the bike was running, and opened it back up when the bike was about to cut out in hopes of stopping it from leaking, but again, no good.

Any recommendations?

Also, the stock air box is a PAIN IN THE ASS. It is an unbelievably tight fit. I'm thinking I may just get pod filters to clear up some space, but I've read it can be hard to tune the carbs properly.

Any thoughts?? I could reaaaaaaally use the help. :) Thanks!
 
Could it be your float needle valves? I had to replace those on mine. Also, make sure your floats are set properly by adjusting the metal tangs on the hinge of the float (if you have those).

The stock airbox will never NOT be a pain in the ass. It will always suck, but apparently its easier to deal with than getting the engine to run properly with pods. At least thats what I've read a bajillion times.
 
Plus one on the stuck float needle / seat. Might just have a hunk of crap not letting it close completely.
www.CB750C.com stongly recomends not using pods on these carbs. The vacuum piston will not respond properly to throttle changes in these Keihins withought the restriction built into the factory airbox... or so they say
No personal experiance yet, but I got a rack of Mikuni's for mine just in case. ;)
 
Spalding said:
Could it be your float needle valves? I had to replace those on mine. Also, make sure your floats are set properly by adjusting the metal tangs on the hinge of the float (if you have those).
The stock airbox will never NOT be a pain in the ass. It will always suck, but apparently its easier to deal with than getting the engine to run properly with pods. At least thats what I've read a bajillion times.

Hoosier Daddy said:
Plus one on the stuck float needle / seat. Might just have a hunk of crap not letting it close completely.
www.CB750C.com stongly recomends not using pods on these carbs. The vacuum piston will not respond properly to throttle changes in these Keihins withought the restriction built into the factory airbox... or so they say
No personal experiance yet, but I got a rack of Mikuni's for mine just in case. ;)

I'm not sure. I know that I just had the carbs cleaned and rebuilt. I don't see why the float needle would be sticking? Do I need to take the carbs completely off to check the float needles? The float bowl is the bottom of the carbs, right? Can I just let the bike run with the fuel valve off, let it cut out, and undo the float bowl while on the bike? I'm very new to this carb thing, unfortunately.. lol!

Hoosier Daddy: Which bike did you get the Mikuni's for?
 
Nope, not on these. The needle and seat are pointed up into the carb body. The float pivot pin is between two towers that are pretty fragile and could be a bitch to remove with the carbs on the bike. But if you remove the float bowl everything will drop to it's lowest and give you acess to flush the seat with some carb cleaner.Now if the float height is set too high, that could not let it seat and cause your problem too.
The Mikunis came as a spare set for the Suzuki "Overkill" that I didn't need. Don't know if they would work easily on my '81 CB750C "Rock-it" or not. Just have them in a box on the shelf...
 
If you are new to these kind of carbs, you need to spend a little time and educate yourself.
There are a lot of small, but crucial parts that need to be handled and cleaned the right way.
Unless you are really wealthy, it is most cost effective to teach yourself how to clean and set them up.


Once you know how, it really not that hard. However the first time to pull them apart into the MANY pieces it can be intimidating.


Yes, the stock airbox is a huge PAIN. There are some tricks that may help, like taking off the airbox to carb boots by collapsing them back into the airbox.
the bike will be much more reliable with the stock system, however.


There's lots of great info on this site. Use the search button aggressively and read up.


At a guess your fuel issues is likely float height/needle valve related.
All it takes is a little piece of sediment in the tank to get fed into the carbs, and then things get unhappy.
This is why sitting around can be bad for old bikes. In general the more they are ridden, the more reliable they are.


Take your time, and enjoy the journey!
 
You guys are amazing! THANK YOU so much for the help. I greatly appreciate it.

As of now, she runs and runs like a raped ape! :) This thing is FAST. It does not leak gas when it is running. If I forget to close the fuel valve after turning it off, it will leak after a minute or two. I'm not sure if your supposed to close the fuel valve or not, but I've been doing it every time I turn it off. :) I remember I had to manually close the petcocks on my XS850 after turning it off, so perhaps this is the same? Who knows..

Now, I just need to sync the carbs. Ordered a carb sync tool. Never done it before, but my Clymers manual has a detailed description on how to do it, so it shouldn't be to bad.. hopefully! :) Ordered a pair of front caliper rebuild kits. Never done that before either, so it should be a nice learning process.. lol. Pics to come soon!
 
man i am glad to hear she is runnign strong... the fact it still leaks makes me still think float, but kill the pet cock when your done running it, run a tank w/ sea foam every other tank and stretching her legs make stop that issue... on the sync... when i first did it i was a bit confused... but after you get the pattern... your money! I sync mine every 3 or 4 thousand miles, i notice a huge diff when they are dialed in on MPG for my sport touring... hahaha i know MPG... but that is what i ride it for
 
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